3GPP Release 10 (LTE-Advanced) defines a mode in which a physical uplink shared channel PUSCH) and a physical uplink control channel (PUCCH) are simultaneously transmitted on the same subframe. In this mode, a mobile station (user equipment (UE)) is allowed to simultaneously transmit the PUSCH and the PUCCH in the same subframe. The PUSCH is an uplink physical channel mainly used for transmitting user data. The PUCCH is an uplink physical channel used for transmitting layer 1/layer 2 control signals, such as channel quality information (CQI), a rank indicator (RI), cyclic redundancy check (CRC) results, and a hybrid automatic repeat request acknowledgement (HARQ-ACK).
In addition, the 3GPP Release 10 defines carrier aggregation (CA) in which a mobile station communicates with a base station (an eNB) simultaneously using a plurality of carriers in either or both of an uplink and a downlink. Each carrier used for carrier aggregation is called a component carrier (CC). That is, when the CA is used, there is a plurality of serving cells, and each serving cell corresponds to each component carrier. RRC connection between an eNB and a UE is provided in one serving cell, i.e., a primary serving cell. A component carrier of the primary serving cell is called a primary component carrier (PCC). Other serving cells are called secondary serving cells, and a component carrier of each secondary serving cell is called a secondary component carrier (SCC). A PUCCH is transmitted on an uplink PCC. Meanwhile, a PUCCH is not transmitted on an uplink SCC. One or more secondary serving cells (SCCs) are activated (added) and deactivated (deleted) as necessary. A system bandwidth of one component carrier is a maximum of 20 MHz. Since the 3GPP Release10 specifies CA of up to 5 component carriers, each of an uplink and downlink bandwidth can be extended up to 100 MHz.
Further, in the 3GPP Release 10, the UE that supports uplink CA and supports simultaneous transmission of a PUSCH and a PUCCH performs extended Power Headroom Reporting (PHR) (see Sections 5.4.6 and 6.1.3.6 of Non-Patent Literature 1). The extended PHR includes UE's maximum transmission power information PCMAX, c(k) and power headroom level information PHc(k) regarding each of activated uplink component carriers.
Specifically, two types of power headroom are defined in order to deal with the simultaneous transmission of the PUSCH and the PUCCH. The type-1 power headroom corresponds to a case where only a PUSCH is transmitted on an uplink component carrier, and it is calculated by the following Formula (1):PHtype1,k=PCMAX,k−PPUSCH,k  (1)
where PCMAX, k represents UE's maximum transmission power for the uplink component carrier k, and PPUSCH, k represents estimated PUSCH transmission power for the uplink component carrier k.
The type-2 power headroom corresponds to a case where a PUSCH and a PUCCH are simultaneously transmitted on an uplink component carrier, and it is calculated by the following Formula (2):PHtype2,k=PCMAX,k−PPUSCH,k−PPUCCH,k  (2)
where the PCMAX, k and the PPUSCH, k are the same as those defined in relation to Formula (1), and PPUCCH, k represents estimated PUCCH transmission power for the uplink component carrier k.
As already mentioned, a secondary serving cell does not transmit a PUCCH. Accordingly, a secondary serving cell (i.e., a secondary component carrier (SCC)) always reports a type-1 PHR. Meanwhile, a primary serving cell transmits a PUCCH and a PUSCH. Accordingly, a primary serving cell (i.e., a primary component carrier (PCC)) reports a type-1 power headroom or a type-2 power headroom. Specifically, a primary serving cell reports a type-2 PHR, when simultaneous transmission of a PUCCH and a PUSCH is configured.
FIGS. 1 and 2 show power headroom of each component carrier when carrier aggregation of two uplink component carriers UL_CC#1 and UL_CC#2 is performed. FIG. 1 shows an example in which each of the UL_CC#1 and the UL_CC#2 transmits a type-1 PHR. Meanwhile, FIG. 2 shows an example in which the UL_CC#1 (i.e., the PCC) is configured to transmit a PUCCH and a PUSCH simultaneously and reports the type-2 PHR. As is apparent from FIGS. 1 and 2 and the above-mentioned Formulas (1) and (2), power headroom means a transmission power margin of a UE.